This study examined the convergent validity of a computerized use of time diary (MARCA) relative to pedometry. Participants aged 9-16 years wore a pedometer and completed the MARCA. Comparing pedometer data and self-report data collected for the same day (n = 297 participants), the correlation (Spearman's rho) with PAL was 0.54 and with MVPA was 0.50. Comparing mean daily step counts over 6-7 days with averaged self-report data collected on different days (n = 1713 participants) Spearman's rho for PAL was 0.45 and for MVPA was 0.44. Thus, the MARCA showed validity similar or superior to most self-report instruments for young people.